The present invention relates to the field of receivers (preferably transceivers) in which synchronizing pulses are used to coordinate the serial transmission and reception of information in a time shared multiplex system.
In prior multiplexing systems it is necessary to synchronize the transmission and reception of information along a common data line. This means that switching circuits must be utilized at both ends of the data line to insure that when one type of data is transmitted from one end of the data line it is received by the correct receiving circuitry at the other end of the data line. This is generally accomplished by supplying a timing clock signal along a conductor line separate from the common data line. Generally the timing clock signal includes a synchronization pulse for initializing switching circuitry at at least one end of the common data line. After the synchronization pulse additional signalling pulses then follow which are utilized to control the switching circuits at both ends of the data line. This technique is commonly used in time shared multiplexing systems.
To identify the existence of a synchronization pulse, various synchronizing pulse detectors have been utilized. Some systems depend upon the amplitude of the timing clock signal for controlling various timing functions, and therefore to determine the occurrence of a synchronization pulse these systems use an amplitude comparator as a detector to determine when the timing clock signal has a specified amplitude. An example of such a synchronizing pulse detector is illustrated in paper number 760181 presented at the Society of Automotive Engineers, Feb. 23-27, 1976, entitled "Time-Shared Multiplexing System Applied to Motor Vehicles". Other synchronizing pulse detectors identify the synchronizing pulse by attempting to calculate the duration of the synchronizing pulse wherein the synchronizing pulse duration is longer than other timing pulses, if other timing pulses exist. A common example of this other type of synchronizing pulse detector would be the vertical synchronizing pulse detector commonly used for television reception. In this type of detector the existence of the vertical synchronizing pulse is determined by performing an amplitude integration during the time that the synchronizing pulse occurs.
Both of the above discussed prior art synchronizing pulse detectors are subject to false detections of the synchronizing pulse since they are both sensitive to amplitude variations of the synchronizing pulse. Certainly the first prior system which is totally dependent upon the amplitude of the received timing clock signal is extremely susceptible to all variations in the amplitude of the timing clock signal. Similarly, the television synchronizing pulse detector is also sensitive to the amplitude of the received synchronization pulse since if the pulse amplitude momentarily disappears due to a noise pulse the integration ceases or proceeds in a reverse direction. This result is responsible for in the rolling of television pictures during extremely noisy conditions since proper identification of the vertical synchronizing pulse is not occuring.
In a transceiver where channel select information is multiplexed between a remote control unit and a main chassis, improper identification of a synchronization pulse could result in selection of and/or transmission on the wrong channel. This would result in lost reception or transmission of messages and therefore must be prevented at all cost.